HCS412I MICROCHIP [Microchip Technology], HCS412I Datasheet - Page 13

• Manufacturer Part Number: HCS412I
• Description: KEELOQ Code Hopping Encoder and Transponder
• Manufacturer: MICROCHIP [Microchip Technology]

FIGURE 3-5:
FIGURE 3-6:
3.4
3.4.1
The code word completion feature ensures that entire
code words are transmitted, even if the active button is
released before the code word transmission is com-
plete. If the button is held down beyond the time for one
code word, multiple complete code words will result.
The device default is that a momentary button press
will transmit at least one complete code word. Enable
the Minimum Four Code Words (MTX4) configuration
option to extend this feature such that a minimum of 4
code words are completed on a momentary button acti-
vation.
2002 Microchip Technology Inc.
TOTAL TRANSMISSION:
TOTAL TRANSMISSION:
Encoder Special Features
CODE WORD COMPLETION AND
MINIMUM CODE WORDS
31 RFT
50% Duty
Preamble
Long Preamble (LPRE) disabled
PWM TRANSMISSION FORMAT—MOD = 0
MANCHESTER TRANSMISSION FORMAT—MOD = 1
E
Preamble, 50% Duty Cycle
START bit
Header
bit 0 bit 1 bit 2
Preamble Sync Encrypt
Preamble
Encrypted
Portion
LOGIC "0"
LOGIC "1"
Sync
Preliminary
Header
1 CODE WORD
10T
CODE WORD
Encrypt
1 CODE WORD
E
LOGIC "0"
LOGIC "1"
CODE WORD
Fixed
Fixed
3.4.2
The Auto-shutoff function prevents battery drain should
a button get stuck for a long period of time. The time
period (T
the device will enter Time-out mode.
The device will stop transmitting in Time-out mode but
there will be leakage across the stuck button input’s
internal pull-down resistor. The current draw will there-
fore be higher than when in Standby mode.
3.4.3
Federal Communications Commission (FCC) part 15
rules specify the limits on worst case average funda-
mental power and harmonics that can be transmitted in
a 100 ms window. For FCC approval purposes, it may
therefore be advantageous to minimize the transmis-
sion duty cycle. This can be achieved by minimizing the
on-time of the individual bits as well as by blanking out
consecutive code words.
T
Encrypted
E
Portion
Fixed Code
T
T
Portion
E
Guard
E
Guard
AUTO-SHUTOFF
CODE WORD BLANKING ENABLE
TO
T
T
E
E
) is approximately 20 seconds, after which
Preamble
Preamble Sync
STOP bit
Fixed Code
Sync
Portion
Encrypt
Guard
Time
Encrypt
HCS412
DS41099C-page 13
Guard
Time